William MacMillan
William MacMillan or McMillan may refer to:
- Bill MacMillan (born 1943), hockey player and coach
- William Duncan MacMillan (1871–1948), American mathematician and astronomer
- William J. P. MacMillan (1881–1957), Canadian physician and Prince Edward Island politician
- William McMillan (congressman) (1764–1804), delegate to the United States Congress from the Territory Northwest of the River Ohio
- William McMillan (college president) (1777–1833), president of Jefferson College, 1817–1822
- William McMillan (sculptor) (1887–1977)
- William McMillan (Australian politician) (1850–1926), Irish-Australian politician, first Member for Wenthworth
- William McMillan (sport shooter) (1929–2000), American sports shooter and Olympic Champion
- William Hector McMillan (1892–1974), Liberal party member of the Canadian House of Commons
- Billy McMillan (died 1991), Irish footballer
- William McMillan (footballer), footballer in the late 1890s
- William Macmillan (Moderator) (1927–2002), minister of the Church of Scotland
- William Miller Macmillan, Scottish historian